The heat lamps used in the beverage bottle industry typically are quartz lamps at a temperature of 3000-4000.degree. F. with a broad emission spectrum from 500 nm to greater than 1500 nm. The emission maximum is around 1100-1200 nm typically. Polyester, especially PET absorbs poorly in the region between 500 and 1400 nm. Since compounds with absorbances in the range of 400-700 nm appeared colored to the human eye, compounds which absorb in this range will impart color to the polymer. Thus to improve the reheat rate of a material, one must increase the absorption of radiation in the region of emission of the heat lamps, preferably in the region of maximum emission. Many methods exist for accomplishing this.
U.S. Pat. Nos. 4,408,004, 4,476,272, 4,535,118, 4,420,581, 5,419,936, and 5,529,744, disclose various gray or black body absorbing compounds which are disclosed to improve reheat rates. Disclosed compounds include finely divided carbon black, iron oxides and antimony metal. All of these compounds are black or gray body absorbers which absorb energy across the whole spectrum of infrared and visible radiation. As a result, these materials all impart a grayness or loss of transparency to the polymer which is in proportion to the amount of material added to the polymer. To some extent, this effect can be controlled by varying the particle size of the additive, but it cannot be eliminated.
U.S. Pat. No. 4,481,314, discloses the use of certain anthraquinone type dyes for the purposes of improving reheat rates. However, these dyes have substantial absorbance in the visible spectrum resulting in coloration of the polymer. In addition, their relatively low molar extinction coefficients (.epsilon.) (in the range of 20,000) require the use of relatively large amounts of the dye (20-100 ppm) to the polymer. At the level of 50 ppm, the reheat rate improvement was 7%. However, at these levels the polymer displays a light green color which is not suitable for producing clear bottle polymer resin.